Tapio Rajala

Riemannian Ricci curvature lower bounds in metric measure spaces with -finite measure

In prior work (4) of the first two authors with Savare, a new Riemannian notion of lower bound for Ricci curvature in the class of metric measure spaces (X,d,m) was introduced, and the corresponding class of spaces denoted by RCD(K,∞). This notion relates the CD(K,N) theory of Sturm and Lott-Villani, in the case N = ∞, to the Bakry-Emery approach. In (4) the RCD(K,∞) property is defined in three equivalent ways and several properties of RCD(K,∞) spaces, including the regularization properties of the heat flow, the connections with the theory of Dirichlet forms and the stability under tensor products, are provided. In (4) only finite reference measures m have been considered. The goal of this paper is twofold: on one side we extend these results to general σ-finite spaces, on the other we remove a technical assumption appeared in (4) concerning a strengthening of the CD(K,∞) condition. This more general class of spaces includes Euclidean spaces endowed with Lebesgue measure, complete noncompact Riemannian manifolds with bounded geometry and the pointed metric measure limits of manifolds with lower Ricci curvature bounds.

Existence of doubling measures via generalised nested cubes

Working on doubling metric spaces, we construct generalised dyadic cubes adapting ultrametric structure. If the space is complete, then the existence of such cubes and the mass distribution principle lead into a simple proof for the existence of doubling measures. As an application, we show that for each

Euclidean spaces as weak tangents of infinitesimally Hilbertian metric measure spaces with Ricci curvature bounded below

\epsilon>0

Packing dimension of mean porous measures

there is a doubling measure having full measure on a set of packing dimension at most

UPPER CONICAL DENSITY RESULTS FOR GENERAL MEASURES ON R-n

\epsilon

Local homogeneity and dimensions of measures

.

Planar Sobolev homeomorphisms and Hausdorff dimension distortion

We show that in any infinitesimally Hilbertian CD � (K,N)-space at almost every point there exists a Euclidean weak tangent, i.e. there exists a sequence of dilations of the space that converges to a Euclidean space in the pointed measured Gromov-Hausdorff topology. The proof follows by considering iterated tangents and the splitting theorem for infinitesimally Hilbertian CD � (0,N)-spaces.

Local multifractal analysis in metric spaces

We prove that the packing dimension of any mean porous Radon measure on Rd may be estimated from above by a function which depends on mean porosity. The upper bound tends to d . 1 as mean porosity tends to its maximum value. This result was stated in D. B. Beliaev and S. K. Smirnov [�eOn dimension of porous measures�f, Math. Ann. 323 (2002) 123.141], and in a weaker form in E. J�Narvenp�Na�Na and M. J�Narvenp�Na�Na [�ePorous measures on Rn: local structure and dimensional properties�f, Proc. Amer. Math. Soc. (2) 130 (2002) 419.426], but the proofs are not correct. Quite surprisingly, it turns out that mean porous measures are not necessarily approximable by mean porous sets. We verify this by constructing an example of a mean porous measure �E on R such that �E(A) = 0 for all mean porous sets A �¼ R.

Restricting open surjections

We study conical density properties of general Borel measures on Euclidean spaces. Our results are analogous to the previously known result on the upper density properties of Hausdorff and packing-type measures.

A Density Result for Homogeneous Sobolev Spaces on Planar Domains

We introduce two new concepts, local homogeneity and local L^q-spectrum, both of which are tools that can be used in studying the local structure of measures. The main emphasis is given to the examination of local dimensions of measures in doubling metric spaces. As an application, we reach a new level of generality and obtain new estimates in the study of conical densities and porous measures.